1. Field of the Invention
The present invention relates to a plasma generating apparatus, and more specifically, to a plasma generating apparatus which can be used in a radar system and which generates a sheet plasma that can be used as a reflecting mirror for electromagnetic waves.
2. Description of the Background Art
A radar system in which a sheet plasma is used as a reflecting mirror for electromagnetic waves is disclosed in U.S. Pat. Nos. 5,182,496 and 5,814,942. These references describe a method and a device for generating a sheet plasma by applying a high voltage between a cathode and an anode.
One angle control method for the sheet plasma is described in an article from IEEE AES System Magazine (October, 1996, p. 38). This article describes a control method setting the sheet plasma at a desired elevation angle with convention electromagnetic coils.
Moreover, Japanese Patent Laying-Open No. 11-087091 discloses a control method in which a laser beam irradiates a cathode at different angles and in which secondary electrons emitted from the cathode aid the plasma generation as well as set a desired azimuth.
The above-described conventional angle control of the sheet plasma involves the following problems since an electromagnetic coil and a laser are required.
Angle control of a sheet plasma by the combination of a plurality of electromagnetic coils presents the problem of increased complexity and size of the device. In addition, when providing a large number of electromagnetic coils in order to improve the angle precision, the effective area of the antenna serving as a plasma mirror is reduced so that the antenna gain is decreased. Further, when a laser is used for angle control of the sheet plasma, the provision of a plurality of lasers in the periphery of the cathode to improve precision results in an unfavorable increase in the device size.
The present invention is made to solve the above problems, and an object of the present invention is to perform the angle control of a sheet plasma with a simple configuration.
According to one aspect of the present invention, the plasma generating apparatus includes a chamber, an anode, a cathode, a power supply, and first and second switching elements. The anode is provided within the chamber, and includes a plurality of first electrodes. The cathode is provided within the chamber, and includes a plurality of second electrodes. From the power supply, a voltage is applied to first and second electrodes to form a sheet plasma that reflects the directional electromagnetic waves. The first and second switching elements switch between the groups of the first and second electrodes to which the voltage from the power supply is applied so as to change the angle and the shape of the sheet plasma. The first and second electrodes, for instance, are respectively arranged in a matrix. Moreover, the angle of the sheet plasma herein refers to the angle of the sheet plasma relative to the electromagnetic waves that enter the plasma generating apparatus.
Since the first and second switching elements are provided to the plasma generating apparatus as described above, certain groups of first and second electrodes to which a high voltage is applied can be switched to other groups of first and second electrodes, for example. Thus, the position in which the sheet plasma is formed and the angle of the sheet plasma relative to the electromagnetic waves can be changed so that not only the angle control but also the shape control of the sheet plasma can be performed.
According to another aspect of the present invention, the plasma generating apparatus includes a chamber, an anode, a cathode, a power supply, and a driving element. The anode and the cathode are provided within the chamber. From the power supply, a voltage is applied to the anode and the cathode to form a sheet plasma between the anode and the cathode that reflects the directional electromagnetic waves. The driving element drives at least one of the anode and the cathode to change the angle of the sheet plasma. Examples of the driving element include a rotation mechanism for rotating at least one of the anode and the cathode, and a tilting mechanism for tilting at least one of the anode and the cathode.
By providing a driving element as described above, at least one of the anode and the cathode can be driven. As a result, the angle of the sheet plasma formed between the anode and the cathode can be controlled. For instance, the angle control of the sheet plasma in the azimuth direction can be performed by rotating the anode or the cathode. Moreover, the angle control of the sheet plasma in the direction of elevation angle can be performed by tilting the anode and the cathode by a prescribed angle.
According to a further aspect of the present invention, the plasma generating apparatus includes a chamber, an anode, a cathode, a power supply, first and second magnets, and a magnet driving element. The anode and the cathode are provided within the chamber. From the power supply, a voltage is applied to the anode and the cathode to form a sheet plasma between the anode and the cathode that reflects the directional electromagnetic waves. The first magnet is provided on the anode, and the second magnet is provided on the cathode. The magnet driving element drives at least one of the first and second magnets to change the angle of the sheet plasma. The magnet driving element, for instance, includes a rotation mechanism for rotating at least one of the first and second magnets, and a moving mechanism for shifting at least one of these first and second magnets. Moreover, a typical example of the magnet is a permanent magnet.
By providing a magnet driving element as described above, a magnet can be rotated or shifted on an anode and a cathode. Thus, the direction of magnetic field lines and the position in which the magnetic field lines are generated can be changed such that the angle control of the sheet plasma can be performed.
In the above aspects of the present invention, the voltage, for instance, is a pulse voltage, a radio-frequency voltage, or a direct current voltage. In addition, the shape of at least one of the cathode and the anode is typically a flat-plate shape. At least one of the opposing surfaces formed by the cathode and the anode may be a curved surface, however. For instance, both of the opposing surfaces formed by the cathode and the anode may form paraboloids. In this case, the sheet plasma can be angle-controlled in the direction of the elevation angle.
According to a still further aspect of the present invention, the plasma generating apparatus includes a chamber, an anode, a cathode, a dielectric, a radio-frequency power supply, and a dielectric driving element. The dielectric is provided within the chamber. The high-frequency power supply applies a high frequency to the dielectric so as to form on a surface of the dielectric a sheet plasma that reflects the directional electromagnetic waves. The dielectric driving element drives the dielectric to change the angle of the sheet plasma.
A surface wave plasma can be formed on a surface of a dielectric plate by propagating a high frequency electromagnetic wave in the dielectric plate. In order to propagate the electromagnetic wave in the dielectric plate, for instance, a high-frequency power supply and a high-frequency transmission system may be provided. The surface wave plasma forms the sheet plasma of the present invention. By providing a dielectric driving mechanism for driving the dielectric plate, the dielectric plate can be tilted or rotated so that the sheet plasma can be angle-controlled not only in the azimuthal direction but also in the direction of the elevation angle.
Preferably, a member formed of a high-frequency electromagnetic wave non-absorbing material (for instance, a metal plate) or a high-frequency electromagnetic wave absorbing material is provided on one surface of the dielectric. Thus, the formation of the surface wave plasma on one surface can be prevented, and a sheet plasma of the desired density can be obtained at a low power.
In addition, the surface of the dielectric on which the sheet plasma is to be formed may be a curved surface. As a result, a sheet plasma having a parabolic shape, for instance, can be formed, facilitating the selection of the setup positions of a transmitter and a receiver.
According to a still another aspect of the present invention, the plasma generating apparatus includes a chamber, an anode and a cathode, a power supply, a high-frequency electromagnetic wave supply element, and a moving mechanism. The anode and the cathode are provided within the chamber. From the power supply, a voltage is applied to the anode and the cathode to form a low-density plasma between the anode and the cathode. The high-frequency electromagnetic wave supply element supplies a high-frequency electromagnetic wave into the low-density plasma so that a high-density sheet plasma that reflects the directional electromagnetic waves is formed. The moving mechanism moves the high-frequency supply electromagnetic wave element to change the position in which the high-density sheet plasma is formed. Examples of the high-frequency electromagnetic wave supply element include a high-frequency power supply and a high-frequency electromagnetic wave radiation antenna. In this case, the position of the high-frequency electromagnetic wave radiation antenna is shifted by the moving mechanism.
By propagating a high-frequency electromagnetic wave into the low-density plasma and allowing the high-frequency electromagnetic wave to be absorbed by the low-density plasma as described above, a high-density sheet plasma can be formed. This high-density sheet plasma can reflect the directional electromagnetic waves. By providing the moving mechanism, the high-frequency supply element can be moved so that the position in which the high-density sheet plasma is formed can be changed as a result. Thus, the angle control of the sheet plasma can be performed.
According to a still further aspect of the present invention, the plasma generating apparatus includes a chamber, an anode and a cathode, a power supply, and a plurality of high-frequency supply elements. The anode and the cathode are provided within the chamber. From the power supply, a voltage is applied to the anode and the cathode to form a low-density plasma between the anode and the cathode. The plurality of high-frequency supply elements supply a high-frequency electromagnetic wave into the low-density plasma so as to form a high-density sheet plasma that reflects the directional electromagnetic waves.
By providing a plurality of high-frequency supply elements as described above, a desired high-frequency supply element alone can be operated selectively. Thus, the angle control of the high-density sheet plasma can be performed.
According to a still another aspect of the present invention, the plasma generating apparatus includes a chamber, an electron beam source, a metal plate, a nozzle, and a nozzle driving element. The electron beam source supplies the electron beam into the chamber. The metal plate is provided within the chamber. The nozzle directs the electron beam toward the metal plate so that a sheet plasma that reflects the directional electromagnetic waves is formed. The nozzle driving element drives the nozzle to change the angle of the sheet plasma.
By providing the nozzle driving element as described above, the nozzle can be rotated or tilted. Thus, the electron beam plasma can be jet out in any desired direction so that the angle control of the sheet plasma can be performed.
According to a still further aspect of the present invention, the plasma generating apparatus includes a chamber, a plasma source, a metal plate, a nozzle, and a nozzle driving element. The plasma source supplies a plasma into the chamber. The metal plate is provided within the chamber. The nozzle directs the plasma toward the metal plate so as to form a sheet plasma that reflects the directional electromagnetic waves. The nozzle driving element drives the nozzle to change the angle of the sheet plasma.
In the above aspect, since the nozzle can be rotated or tilted, the plasma can be jet out in any desired direction so that the angle control of the sheet plasma can be performed.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.